This invention relates to lighting devices of the type generally used by dentists for illuminating the oral cavity of a patient during the performance of dental or surgical procedures. Such devices are generally constructed with reflectors in the form of portions of elipsoids of revolution, i.e., surfaces formed by revolving an elipse about a major axis. A light source is located transverse to the axis of the elipsoid at one focus thereof, while the device is oriented such that the oral cavity of the patient is in the vicinity of the conjugate focus. It has been customary to employ in such devices, light sources having filaments elongated in directions transverse to the major axis of the reflector. Due to the transverse extent of the filament, a light pattern of somewhat elongated width has been formed in the area of the conjugate focus. It has been found however that it is necessary to modify the shape of the reflector surface and the filament geometry in order to enhance the pattern of the beam.
Modification of the shape and geometry of the filament has provided helpful but is not a complete solution to the requirements for producing intense pattern of light in the vicinity of the desired zone of illumination, i.e., the patient's oral cavity.
Modification of the reflector surface has also proved useful, but stray light rays commonly known as "fishtails" have been produced by the modified shape of the reflector. One of the reasons for the production of such fishtails is that the basic reflector surface has been modified so that it does not in all respects behave as a mathematical model. For example in a true elipsoid, a ray leaving the primary focus and striking any surface of the elipsoid will be reflected through the conjugate focus. Since no reflector surface is perfect and since no ideal point source is available, the pattern about the conjugate focus will be somewhat distorted. Generally however, the pattern will be concentrated. By elongating the filament along the various axes of the elipsoidal surface, or by distorting the shape of the elipsoid itself, variations in the width, height, and depth of the light pattern at the conjugate focus can be produced. These efforts however have not been accurately predictable and they are based many times upon approximations and emperical trials.
The present invention provides for a modification of the reflector surface such that a predictable pattern will be produced which pattern can be changed by variations in the parameters which have been developed in connection with the present invention.